1. Field of the Invention
The present invention relates generally to power driven saws and, more particularly, to a load and speed control apparatus for use on such saws in preventing a movable carriage provided on the saw from kicking radially outward toward an operator during a sawing operation.
2. Discussion of the Prior Art
Radial arm saws are commonly used by carpenters and craftsmen to perform a variety of wood working operations. An example of one such type of saw is the Sears/Craftsman 10" Radial Saw, which includes, among other features, a support frame for supporting the apparatus on the floor of a workshop or the like, and a mounting arm having a vertical pivot axis and means for mounting the arm on the frame for pivotal movement about the pivot axis. A carriage is mounted on the arm for radial movement along the arm relative to the pivot axis, and a saw blade is supported on the carriage for rotational movement relative to the carriage such that a power means may be actuated to rotate the saw to carry out a sawing operation. Of course, numerous companies market similar saws, and the problems discussed below are experienced in the use of these other available devices.
By providing a saw having a radial arm for use in supporting the saw blade and carriage, an apparatus results which is extremely versatile. For example, because the carriage is movable along the arm in the radial direction of the pivot axis, and due to the construction of the arm which permits the arm to be pivoted relative to the frame, it is possible to run the saw blade over a work table of the frame at any desired angle relative to the pivot axis. Thus, crosscuts at any desired angle may be made consistently by simply orienting the arm at the desired angle and moving the carriage in the radial direction of the arm.
Further, by providing for rotational movement of the carriage relative to the arm, the saw blade may be oriented for rotation about an axis extending in a direction parallel to the direction in which the arm extends such that rip sawing is possible. In such applications, wood is passed lengthwise beneath the carriage and saw blade while the blade is rotating such that a lengthwise cut is made without the carriage being moved.
A common problem experienced during the use of radial saws in making crosscuts includes the tendency of the carriage of such saws to kick away from the pivot axis of the arm toward an operator when the rotating blade encounters resistance in the material being cut. This kicking action of the carriage is a result of the moment force exerted on the carriage by the rolling action of the blade which occurs when the blade encounters such resistance, and can create serious safety risks to the operator. For example, when the carriage kicks toward the operator during a sawing operation, it is possible that the operator will be unprepared for such movement and may have their hand in the path of the blade such that injury would result from the unexpected carriage movement.
In an attempt to overcome this common problem, U.S. Pat. No. 4,590,831, to Brodin, illustrates the use of a radial arm saw having hydraulic stroke control means for controlling the speed of cut of the saw through work pieces positioned on a work table. The stroke control means includes a hydraulic cylinder having ports at either end thereof and a piston disposed between the ports and connected for movement with the carriage of the saw. The ports are connected to one another by a connection line that is provided with a valve for controlling the flow of fluid from one port to the other. The valve includes a pivotal lever for continuously adjusting the flow rate of fluid therethrough in order to set the control rate of the speed of the carriage.
Another patent illustrating the use of a device attempting to overcome the problem of kicking of the saw carriage away from the pivot axis of the arm during a sawing operation, is shown in U.S. Pat. No. 4,870,882, to Faxon Sr., wherein a radial arm saw control mechanism is provided with a piston and cylinder assembly having fluid flow means associated therewith for controlling movement of a radial arm saw toward and away from an operator.
Any control mechanism constructed in accordance with either of these two noted patents operates to restrain all movement of the saw by requiring the saw movement to be accompanied by the movement of a piston within the cylinder and of fluid which must pass through a by-pass conduit having an adjustable valve. Thus, the saw operator must always pull on the saw carriage against the full restraining force of the control mechanism in order to carry out a sawing operation.